Over recent times the use of liquid crystal display devices has spread rapidly not only in information and telecommunications equipment but in electronic equipment in general. Since these liquid crystal display devices do not themselves emit light, most such devices in use are of the transmissive type that has a backlight provided at the back of a substrate.
An ordinary transmissive liquid crystal display device of the related art will now be described with reference to FIGS. 5 and 6. FIG. 5 is a schematic plan view showing in close-up a single pixel portion of the related art liquid crystal display device as seen through the color filter substrate, while FIG. 6 is a cross-sectional view on line VI-VI in FIG. 5.
The related art liquid crystal display device 10A of FIGS. 5 and 6 is composed of an array substrate 11, a color filter substrate 12, and a liquid crystal layer 13 provided between those two substrates. The array substrate 11 comprises: a transparent substrate 31 of glass or similar; multiple scan lines 32 and signal lines 33 that are constituted of conductive substances and are arranged in grid form on the surface of the transparent substrate 31; thin film transistors (“TFTs” below) 34 that are provided close to the intersections of the scan lines 32 and signal lines 33 and serve as switching elements; multiple storage capacitor electrodes 36 that are constituted of a conductive substance and are provided between the scan lines 32 so as to be almost parallel with the scan lines 32; a gate insulator 37 that covers the scan lines 32 and the storage capacitor electrodes 36 and is constituted of inorganic insulator; a protective insulator 38 that covers the signal lines 33 and the TFTs 34 and is constituted of inorganic insulator; an interlayer 39 that is provided over the protective insulator 38 and is constituted of organic insulation film; and pixel electrodes 40 constituted of indium tin oxide (ITO) or similar, which are provided over the interlayer 39, and each of which is positioned so as to cover one of the domains corresponding to one pixel that are enclosed by the scan lines 32 and signal lines 33.
The TFTs 34 are each composed of: a source electrode S that branches off from a signal line 33; a gate electrode G that branches off from a scan line 32; a drain electrode D that is connected to the pixel electrode 40; and a silicon layer 35 that is constituted of polysilicon (p-Si), amorphous silicon (a-Si) or the like. The pixel electrode 40 is connected to the drain electrode D via a contact hole 41 provided in the interlayer 39 located over the storage capacitor electrode 36.
The color filter substrate 12 comprises: a transparent substrate 21 constituted of glass or similar; black matrices (not shown in the drawings) that are constituted of chromium metal or similar and are formed as a grid on the surface of the transparent substrate 21; color filters 22R, 22G, 22B constituted of red (R), green (G) and blue (B) etc., each of which is provided in one of the domains delimited by the black matrices; and common electrodes 23 that are constituted of ITO or the like and provided over the color filters 22R, 22G, 22B. To manufacture the liquid crystal display device 10A, the two substrates 11 and 12 are positioned with their surfaces opposing each other, their like outer edges are stuck together by means of seal material (not shown in the drawings), spacers 14 are placed in the resulting interior space, and such space is filled with liquid crystal, thus forming a liquid crystal layer.
Such a liquid crystal display device is for example set forth in Japanese Laid-Open Patent Publication 2001-188256, which includes techniques for rendering the device's aperture ratio higher. One such technique that has long been publicly known, called “field shield pixel” (FSP) or similar term, enlarges the pixel electrode domains in order to raise the aperture ratio, and involves covering the TFTs over with an organic insulative film and flattening the entire surface prior to formation of the pixel electrodes.
FIG. 7 is a cross section on the line VII-VII in FIG. 5. As FIG. 7 shows, in a related art liquid crystal display device 10A the side and end portions of the pixel electrodes 40, each of which covers a domain corresponding to one pixel, are formed so as to overlap the scan lines 32 and signal lines 33 as viewed from above. The purpose of such overlapping of the pixel electrodes 40 with the scan lines 32 and signal lines 33 is to prevent light leakage from such join portions; more precisely, to prevent light leakage from occurring when light from the backlight of the liquid crystal display device 10A passes through the liquid crystal layer at the portions where the orientation of the crystals is disturbed due to the application of voltage at the pixel electrodes' edges. The scan lines 32 and signal lines 33 normally have an identical width L1 which is approximately 8 μm, while the width L2 of the overlaps with the pixel electrodes 40 is approximately 2 μm in each case.
However, if the pixel electrodes are formed over the scan lines and signal lines, certain electrostatic capacitances Csd, Cgd will be present between the scan lines 32 and signal lines 33 on the one hand and the pixel electrodes 40 on the other, as shown in FIG. 7. If such electrostatic capacitances Csd, Cgd exceed a certain level, crosstalk will occur in the display screen when the liquid crystal display device 10A is driven. Crosstalk is particularly liable to occur around black displays which are displayed on a white background. The occurrence mechanism of such crosstalk is thought to be due to reasons such as described below. Namely, FIG. 8 shows a screen in which crosstalk has occurred, in a liquid crystal display device 10A such as shown in FIGS. 5 to 7. In FIG. 8 a black screen is displayed on a white background, with a point within the white background domain being labeled “X” and points within the domains above and below the black screen, that is, lying on the signal lines, labeled “Y”. The voltage waveforms at such points X and Y are shown in FIG. 9.
As FIG. 9 shows, when a signal is applied to the gate electrode of a TFT, the TFT is driven and writing into the pixel electrode begins. When this happens, the potential of the pixel electrode is maintained for a certain period by the capacitance of the auxiliary electrode (refer to FIG. 9A). The potential for the white display that is written into the pixel electrode during the write period rises and falls together with the amplitude of the opposing electrode potential Vcom throughout the hold period (refer to FIG. 9B). Observing the waveforms of the voltages applied in this state to the signal lines and pixel electrodes at points X and Y, it can be seen that voltage for the white display is continuously applied to the signal lines at the point X portion up until the next write period comes, and that the potential of the pixel electrodes at such point X portion rises and falls with the same amplitude up until the next write period comes (refer to FIGS. 9C and 9D).
If, mid-way through such process, voltage for a black display is applied to the signal lines at the point Y portion, the amplitude of the pixel electrode's potential at the Y point portion will vary, and will continue to do so for as long as such voltage is applied to such signal lines (refer to FIG. 9E). As a result, the effective value of the voltage applied to the liquid crystals will differ at points X and Y, giving rise to a difference ΔV which will manifest as a difference in brightness and cause crosstalk to occur (refer to FIG. 9F).
Thus, in a related art liquid crystal display device 10A such as described above there is the problem that crosstalk occurs as a result of the electrostatic capacitance Cgd that arises between the scan lines 32 and pixel electrodes 40 and the electrostatic capacitance Csd that arises between the signal lines 33 and pixel electrodes 40. To resolve this problem, one can increase the capacitance of the capacitor that is constituted by the portion of overlap between the storage capacitor electrode 36 and the drain electrode D of the TFT 34, in other words the storage capacitor that serves as signal hold capacitance for activation of the active matrix, thereby permitting the electrostatic capacitances Cgd and Csd to be ignored. But in order to increase the storage capacitor it will be necessary to enlarge the area of the storage capacitor electrode 36, which will give rise to the further problem of a fall in the aperture ratio of each pixel, since the storage capacitor electrode 36 is composed of a light-blocking conductive substance.
Furthermore, in the related art liquid crystal display device 10A there is also formed an electrostatic capacitance Csc between the signal lines 33 of the array substrate 11 and the common electrodes 23 of the color filter substrate 12 when the array substrate 11 and the color filter substrate 12 are superposed on each other. Likewise, an electrostatic capacitance is formed between the scan lines 32 and the common electrodes 23. Terming such capacitance Cgc, the equivalent circuits for a single pixel of the liquid crystal display device 10A may be represented as in FIG. 10.
As FIG. 10 shows, the electrostatic capacitances Csc and Cgc exert an adverse effect on the opposing electrode potential Vcom. More specifically, there exists the problem that electrical power is consumed by these electrostatic capacitances Csc and Cgc, with the result that the power consumption of the liquid crystal display device 10A increases.
Moreover, the TFTs used in the liquid crystal display device have the property that when light is shone on them a faint electric current flows through them. When generated, such faint current causes hindrance of the TFT ON/OFF control. In the related art liquid crystal display devices therefore, black matrices for preventing extraneous light from being shone onto the TFTs are deployed over the color filter substrate so as to overlap the TFTs when viewed from above, with the purpose of preventing light leakage to the TFTs. By such means it is possible to curb to a certain extent the shining of extraneous light onto the TFT, but the fact that black matrices are provided over the color filter substrate means that relatively wide gaps are formed between that substrate and the TFTs, with the result that entry of extraneous light from oblique directions cannot be prevented. A further problem is that light from the backlight will shine onto the black matrices, constituted of chromium metal or the like, where some of such light will be reflected and shone onto the TFTs, resulting in light leakage to the TFTs.